The Cirrus system is deployed by rockets, allowing it to function at a very low altitude. They say that you should deploy it no matter what altitude you are at, and it will add at least some friction. The system has a very impressive track record.
However, at this altitude, with an airplane this heavy, you might have to put the rockets on the plane to decelerate enough to save lives.
Wouldn't be able to save a fully-loaded 787 in low & slow conditions because the area of canopies needed to deploy would be several acres. And they'd add several tonnes.
At least it worked for me on Kerbal Space Program. At least sometimes.